Abnormal mechanical function and degenerative change in joints are related. On one hand, there are many examples of mechanical derangement apparently being the primary cause of accelerated degenerative change. On the other hand, symptoms in a joint restrict and modify a patient's voluntary movements and usage of the joint. This kind of behavior modification is examined clinically as a crucial part of the patient assessment and diagnosis in Orthopaedics. Differential diagnosis of painful lumbar spine disorders relies heavily on examination of a patient's spinal movements as well as on detection of radiologic signs of degenerative change, abnormal formation of the spine, or pathological signs of metabolic disorders or malignancy. This proposed study aims to relate radiologic signs of intervertebral joint structure abnormalities and asymmetries to three-dimensional movements of these joints in patients with low back pain. Patients will be selected from those attending a daily low back pain clinic. They will be asked to participate in the study if they have signs and symptoms which are related to "segmental instability", and are being considered for local injection of anesthetic and anti-inflammatory agents into facet joints of the spine. After agreeing to this study, they will have measurements of three-dimensional intervertebral joint motion during flexion of the spine by a biplanar radiographic technique. Relationships between abnormalities or asymmetries of these motions and radiologic and clinical signs will be studied. The effects of bony abnormalities of the spine will be studied by simulating them in cadaver specimens. Measurements of motion in these joints will be made by a method directly analogous to that used for patients. The implications of any abnormal motions will be studied by mathematical models and by direct measurement of disc deformation to validate such models. The significance of this proposed study is that it will investigate relationships between bony abnormalities of the spine and low back pain symptoms and kinematics of intervertebral joints.